The present invention relates to a power transmission device constructed to be able to rotationally drive a hollow, outer shaft and an inner shaft put in the concentric relationship with the outer shaft together and to adjust a rotational position (or phase) of the inner shaft relative to the outer shaft, and a plate-material feeding apparatus that incorporates thereinto the power transmission device.
For example, JP-U-63-170039 describes a power transmission device constructed in a manner described above, and a plate-material feeding apparatus that incorporates thereinto the device.
The plate-material feeding apparatus described in JP-U-63-170039 comprises a pair of rolls that interpose therebetween a plate material to intermittently feed the same in constant-length steps to a press machine, a roll release device that moves the both rolls in a direction away from each other, while no plate material is fed to the press machine, to release a clamping force exerted on a plate material by the both rolls, and a plate-material braking device having a pair of braking pieces that interposingly fix a plate material during a period, during which an operation of feeding a plate material to the press machine is not performed.
The plate-material feeding apparatus described in JP-U-63-170039 uses a pair of braking pieces to interposingly fix a plate material when press working of a plate material is performed in the press machine. With some metal mold devices for press machines, however, positioning of a plate material on a metal mold device can be highly accurately performed by providing a pilot pin on an upper metal mold to make the same project downward therefrom, and inserting the pilot pin into a positioning hole formed beforehand on the plate material just before upper and lower metal molds are put together and press working is performed.
For use as a device that feeds a plate material to such press machine, the plate-material feeding apparatus described in JP-U-63-170039 is constructed to temporarily release clamping of a plate material by the pair of braking pieces just before the plate material having been fed to a press machine is subjected to press working.
The power transmission device incorporated into the plate-material feeding apparatus comprises a hollow outer shaft having a first cam integrally fitted thereon, and an inner shaft having a second cam integrally fitted thereon, the both shafts being rotationally driven together. The first cam actuates the braking pieces so as to interposingly fix a plate material while the operation of feeding a plate material to the press machine is not performed, and the second cam actuates the braking pieces so as to temporarily release a plate material just before the press working of the plate material. Timing, in which the braking pieces temporarily releases a plate material, is adjusted by rotating the inner shaft relative to the outer shaft to regulate a rotational position (that is, phase) of the second cam relative to the first cam.
JP-U-7-26034 describes a material feeding apparatus that feeds a material to a press machine of the type described above, and a power transmission device incorporated thereinto.
In the power transmission device, a first shaft that rotates in synchronism with the operation of the press machine, and a second shaft that drives a cam similar to the second cam to temporarily release a plate material are connected to each other through two planetary gear mechanisms. The planetary gear mechanisms comprise a first sun gear fixed to an inner end of the first shaft, a plurality of first planetary gears that engage with the first sun gear, a second sun gear fixed to an inner end of the second shaft, a plurality of second planetary gears that engage with the second sun gear, and a ring gear having inner teeth that engage with the first and second planetary gears. With the device, when the first shaft is rotationally driven, the second shaft is rotationally driven through the first sun gear, the first planetary gears, the ring gear, the second planetary gears, and the second sun gear. Also, the first shaft and the second shaft can be adjusted in relative rotational positions by using a worm gear to revolve the first planetary gears around the first sun gear.
JP-A-11-77199 also describes a material feeding apparatus that feeds a material to a press machine of the type described above, and a power transmission device incorporated thereinto. The power transmission device described in JP-A-11-77199 is the same as that described in JP-U-7-26034 except that a ring gear is omitted, and constructed to use two planetary gear mechanisms and a worm gear.
The plate-material feeding apparatuses described in JP-U-63-170039, JP-U-7-26034, and JP-A-11-77199 is of a type commonly called a roll feed, in which a plate material is fed by a pair of rolls, while a plate-material feeding apparatus commonly called a gripper feed is also known (see, for example, JP-A-63-82271).
The gripper feed described in JP-A-63-82271 includes a first gripper device having a first stationary upper gripper and a vertically movable, first movable lower gripper interposing therebetween a plate material to intermittently feed the same to a working machine such as a press machine, etc. the gripper feed being constructed to lift a second movable lower gripper, while the operation of feeding a plate material to the working machine is not performed, to have the second movable lower gripper and a second stationary upper gripper interposingly fixing a plate material.
With the power transmission device described in JP-A-63-82271, the inner shaft is rotated relative to the outer shaft to be regulated relative to the outer shaft in position in a direction of rotation, and after the regulation, a clamp screw is used to fix the outer shaft and the inner shaft in a manner to make them non-rotatable relative to each other. Accordingly, there is involved a problem that the regulating work cannot be performed in the operation of the plate-material feeding apparatus and the power transmission device, during which the outer shaft and the inner shaft are rotationally driven.
With the power transmission device described in JP-U-7-26034, the first shaft and the second shaft are adjusted in relative rotational positions by revolving the first planetary gears around the first sun gear, so that it is possible to perform the regulating work also while the power transmission device operates, that is, the first shaft and the second shaft are rotationally driven.
However, the power transmission device incorporates thereinto two planetary gear mechanisms and also needs a worm gear that revolves the first planetary gears around the sun gear. The construction using many gears in this manner is complex and involves a problem that backlash of the gears worsen accuracy in regulation.
The power transmission device described in JP-A-11-77199 involves a similar problem to the above.